1. Field of the Invention
The present invention relates to a radar apparatus for measuring the azimuth and other values of a target from a reflected wave which is reflected on the target, and a failure detection method thereof.
2. Description of the Related Art
A Radar apparatus have been used for measuring the azimuth, distance, velocity etc. of a target by outputting a transmit wave from a transmit antenna and receiving a reflected wave, which is reflected on the target, by a receive antenna. For example, a radar apparatus is installed in a vehicle and used for preventing collision with a vehicle in front.
Some such radar apparatus perform failure detection for detecting the failure of each component in the apparatus.
For example, some radar apparatuses intermittently connect a transmit and receive antenna by a switching unit, detecting predetermined frequency components of high frequency signals which propagate in the line of a receive antenna by a detection unit during this connected period, and identifying the abnormality of functions based on this detection result (e.g. Japanese Patent Application Laid-Open No. H7-198826).
Some radar apparatuses install an auxiliary line in a transmit section and receive section respectively, and perform a wrap test, and judge whether the paths in the auxiliary line are normally operating based on the test signal, which is output from the auxiliary line of the receive section (e.g. Japanese Patent Application Laid-Open No. H5-315996).
Some radar apparatuses receive radio waves from a transmit antenna to a receive antenna using spatial coupling, and check the presence of abnormality by comparing the output data of an analysis processing circuit of a receive section and the modulation characteristic of the output of an oscillation circuit of a transmit section using a collation circuit (e.g. Japanese Patent Application Laid-Open No. 2001-116828).
Some radar apparatuses store a level of noise signals near the transmit signals generated where there is no object, and a level of signals of noise, which is output from a mixer for reception when operation of an amplifier for transmission is stopped, and diagnose whether the FMCW radar fails by comparing both levels (e.g. Japanese Patent Application Laid-Open No. 2001-141805).
And other radar apparatuses time-division multiplexes a diagnosis wave having a known signal waveform close to a beat signal with the beat signal, and diagnose the presence of failure of a frequency analysis unit by collating the frequency analysis result of the diagnosis wave with a known signal waveform (e.g. Japanese Patent Application Laid-Open No. H10-10227).
However installing a separate circuit for failure diagnosis, like Japanese Patent Application Laid-Open No. H7-198826, increases the cost of the entire radar apparatus.
Performing failure diagnosis using transmit and receive antennas, as in Japanese Patent Application Laid-Open No. 2001-116828, makes it difficult to detect failure accurately since isolation among antennas is high.
If failure is diagnosed based on the level of a receive signal of a reflected wave, on the other hand, the diagnosis depends on the size of the target, and it is difficult to distinguish the detection of the target from the generation of failure.